Swash plate type variable displacement compressor utilizing a spool for controlling the inclination

ABSTRACT

A housing has a crank chamber and a plurality of cylinder bores. The housing also has a discharge chamber and a suction chamber, which are communicatable with the cylinder bores. A drive shaft is supported in the housing, and pistons are accommodated in the respective cylinder bores. A swash plate is supported on the drive shaft in such a manner that its inclined angle can be altered, so that the undulation of the swash plate causes the pistons to reciprocate. When this compressor is running with the swash plate set upright, a controller activates an electromagnetic solenoid to supply a lubricating oil to a pressure chamber from an oil-supplying pump. This causes the spool to shift to temporarily hold the swash plate to an inclined position from the upright position.

This application is a 371 of PCT/JP94/01148 filed Jul. 13, 1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a swash plate type variabledisplacement compressor which is used in, for example, an airconditioning system for a vehicle.

2. Description of the Related Art

In general, an electromagnetic clutch is used to connect and disconnectthe power transmission path from the engine to a compressor in arefrigerant circuit installed in a car. When an air conditioning systemis switched on, the electromagnetic clutch is activated and engine poweris transmitted to the compressor via a belt transmission mechanism andthe electromagnetic clutch.

Frequent repetition of the connection and disconnection of theelectromagnetic clutch to the compressor reduces the durability of thecompressor, and also causes the entire refrigerant circuit toinstantaneously vibrate when the compressor is activated.

In addition, whenever an electromagnetic clutch is used, the overallsize and weight of a compressor is inevitably increased. This requiresincreased space to mount the compressor in the engine compartment andmakes the mounting of the compressor difficult. Further, because theelectromagnetic clutch when in action consumes considerable power, thebattery in the vehicle must bear a great load.

As a solution to this shortcoming, a clutchless compressor has beenproposed whose drive shaft is normally rotated with the engine. Whilethe refrigerant gas is circulating between the compressor and theexternal refrigerant circuit, therefore, no significant problem arises.When there is an insufficient amount of the gas discharged to theexternal refrigerant circuit from the compressor, however, thecirculation of the gas is stopped, which may cause insufficientlubrication of the sliding portions in the compressor. A clutchlessswash plate type compressor designed to overcome this problem isdisclosed in Japanese Unexamined Patent Publication No. Hei 3-37378. Inthis compressor, when the discharge of the gas to the externalrefrigerant circuit including an evaporator from the compressor isunnecessary, the valve which is connected to the suction chamber isclosed to reduce the pressure in the suction chamber and the controlvalve for the passage between the discharge chamber and the crankchamber is opened.

When the gas discharge is unnecessary, the swash plate of the disclosedcompressor is moved to have the minimum inclined angle to minimize thepiston stroke. Further, the passage between the external refrigerantcircuit and the compressor is blocked to suppress the load with respectto the rotation of the compressor. The slight reciprocation of eachpiston causes the gas to be discharged to the discharge chamber from theassociated cylinder bore and to further flow into the crank chamber viathe individual sliding portions from the discharge chamber. The gas inthe crank chamber then flows to the suction chamber from which it isdrawn into the associated cylinder bore.

According to the conventional compressor, as is apparent from the above,when the discharge of the gas to the external refrigerant circuit fromthe compressor is unnecessary, a small amount of refrigerant gas iscirculated inside the compressor so that oil suspended in therefrigerant gas lubricates the sliding portions. As the gas in thecompressor simply circulates, the amount of gas to be circulated is notenough to provide a sufficient amount of lubricating oil, causinginsufficient or inadequate lubrication of the individual slidingportions, particularly, in the crank chamber.

Under low temperature conditions as in the winter or the like, when thecompressor is stopped during large displacement operation, a largeamount of gas remains, liquefied in the crank chamber. With this liquidrefrigerant present, even when the compressor is activated, it isdifficult to turn the liquid refrigerant to the gaseous state merely bythe gas circulation in the compressor which is running now with a smalldisplacement. When the liquid refrigerant is circulated in thecompressor, therefore, the oil sticking on the individual slidingportions is washed out. This deteriorates the lubrication in thecompressor and increases the power loss.

SUMMARY OF THE INVENTION

Accordingly, it is a primary objective of the present invention toprovide a clutchless swash plate variable displacement compressor, whichwill overcome the aforementioned conventional shortcomings and canimprove the lubrication performance at the individual sliding portionsin the compressor.

A housing having a crank chamber and a plurality of cylinder bores alsohas a discharge chamber and a suction chamber, which are communicatablewith the cylinder bores. A drive shaft is supported in the housing, andpistons are accommodated in the respective cylinder bores. A swash plateis supported on the drive shaft in the crank chamber in such a mannerthat its inclined angle is changeable, so that the undulation of theswash plate causes the pistons to reciprocate. The compressor furthercomprises a mechanism for temporarily holding the swash plate to aninclined position from an upright position when the compressor isrunning when the swash plate would otherwise be caused to stay upright.

With this structure, it is possible to lubricate components inside thecompressor without intercepting the passage between the compressor andthe external refrigerant circuit when the compressor is running with thezero displacement or a small displacement close to zero.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The invention,together with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is a vertical cross-sectional view of essential portions of aswash plate type variable displacement compressor according to oneembodiment of the present invention;

FIG. 2 is a vertical cross-sectional view showing the overall compressorunder zero-displacement conditions;

FIG. 3 is a horizontal cross-sectional view showing a hinge mechanism;

FIG. 4 is a cross-sectional view taken along the line IV--IV in FIG. 2;

FIG. 5 is a cross-sectional view showing an oil pump;

FIG. 6 is a vertical cross-sectional view showing an electromagneticdirection switching valve, an electromagnetic open/close valve and apressure control valve;

FIG. 7 is a vertical cross-sectional view also showing theelectromagnetic direction switching valve, the electromagneticopen/close valve and the pressure control valve;

FIG. 8 is a vertical cross-sectional view showing the overall compressorwith a large displacement; and

FIG. 9 is a vertical cross-sectional view showing another compressoraccording to this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A preferred embodiment of the present invention will now be describedreferring to the accompanying drawings.

As illustrated in FIG. 2, a front housing 2 is fixed to a cylinderblock 1. A crank chamber 2a is formed in the front housing 2. Aplurality of cylinder bores 1a are formed in the cylinder block 1. Arear housing 3 is secured to the cylinder block 1. A suction chamber 3aand a discharge chamber 3b are defined in the rear housing 3. The fronthousing 2, cylinder block 1 and rear housing 3 constitute the housing ofa compressor.

A drive shaft 4 is rotatably supported in the cylinder block 1 and fronthousing 2 via radial bearings 5 and 6 in such a manner that the driveshaft 4 passes through the crank chamber 2a. A pulley 7 is secured tothe free end portion of the drive shaft 4 outside the compressor. A belt8 is wrapped around the pulley 7, so that the rotation of the engine istransmitted via the belt 8 and pulley 7 to the drive shaft 4.

A rotary plate 9 is secured to the drive shaft 4 inside the crankchamber 2a. A thrust bearing 10 is arranged on the inner wall of thefront housing 2 to receive the thrust load applied to the rotary plate9. A support arm 11, having a hole 11a, is integrally formed with therotary plate 9.

A swash plate support 12 having a spherical surface 12a isreciprocatably supported on the drive shaft 4 along its axial direction.A swash plate 13 is supported on the swash plate support 12 to betiltable along the spherical surface 12a.

A support pin 14 is fitted in the hole 11a of the support arm 11 so asto be rotatable about its own axis, with guide holes 14a formed in bothend portions of the support pin 14, respectively. See FIG. 3. Twoparallel projections 13a are integrally formed at the center portion ofthe swash plate 13 in such a position to sandwich the drive shaft 4. Apair of guide pins 15 and 16 are respectively fixed to the two parallelprojections 13a, and have their free end portions slidably fitted in theguide holes 14a. In this embodiment, the support arm 11, the swash platesupport 12, the guide pins 15 and 16 and the projections 13a allow theswash plate 13 and the rotary plate 9 to rotate together. Together,these components form a hinge mechanism that permits the variableinclination of the swash plate 13.

As shown in FIG. 2, a plurality of pistons 17 are reciprocatably placedin the respective cylinder bores 1a. A pair of shoes 18 are supported byeach piston 17. The peripheral portion of the swash plate 13 ispositioned between the individual shoes 18 of each pair. The undulatingrotation of the inclined swash plate 13 causes the pistons 17 toreciprocate. A stopper 19 is secured to the outer surface of the driveshaft 4. When the swash plate support 12 abuts on the stopper 19, theswash plate 13 is held upright. A step 4a is formed on the outer surfaceof the drive shaft 4 to determine the maximum inclined angle at whichthe swash plate 13 can be positioned.

A valve plate 20 is secured between the cylinder block 1 and the rearhousing 3. As best seen in FIG. 4, a suction hole 20a and a dischargehole 20b are formed in the valve plate 20 in association with eachcylinder bore 1a. A discharge valve 21a and a suction valve 22a areformed in the valve plate 20, and are of the reed valve type. A retainerplate 23 (see FIG. 2) is placed over the valve plate 20. A retainer 23ais formed on the retainer plate 23 in association with each dischargevalve 21a to prevent that discharge valve 21a from opening too much. Asshown in FIG. 1, a center hole 1b is formed in the cylinder block 1. Acylindrical spool 24 is slidably supported on the outer surface of thedrive shaft 4 in the center hole 1b. A lip seal 25 is provided on theinner surface of the center hole 1b between the radial bearing 6 (seeFIG. 2) and the spool 24. A ring 21 is secured to the inner surface ofthe center hole 1b to hold the lip seal 25 in place.

The spool 24 has a large-diameter portion 24a and a small-diameterportion 24b. When the spool 24 is in a retracted position as shown insolid lines in FIG. 1, the outer surface of the large-diameter portion24a contacts the inner surface of the center hole 1b. A pressure chamber26 is formed between the outer surface of the small-diameter portion 24bof the spool 24 and the inner surface of the center hole 1b.

When oil is supplied to the pressure chamber 26 with the large-diameterportion 24a in contact with the inner surface of the center hole 1b, thespool 24 is urged along to the drive shaft 4 and moved forward in thedirection of the swash plate support 12. As a result, the swash platesupport 12 moves in the same direction. This causes the swash plate 13to move from the upright position to the inclined position shown inphantom lines in FIG. 1.

As shown in FIGS. 2 and 5, a trochoid pump 27 is located at the centerof the rear housing 3. As shown in FIG. 5, this pump 27 has inner teeth27a and outer teeth 27b. The inner teeth 27a are rotated by the driveshaft 4. As the inner teeth 27a rotate, the outer teeth 27b rotate inthe same direction at a slower speed than the inner teeth 27a.

As shown in FIG. 5, a clearance 103 formed between the teeth 27a and27b, shifts in the rotational direction of the teeth 27a and 27b. Duringthis shift, the clearance undergoes a change in its volume due to thedifference between the rotational speeds of the teeth 27a and 27b.Through the above-described action, the lubricating oil is led into theclearance 103 from an arcuate suction port 28a and is discharged throughan arcuate discharge port 29a.

A first oil passage 30 is formed axially in the center of the driveshaft 4, as shown in FIG. 2. Branch oil passages are formed at aplurality of points of the first oil passage 30 allowing oil to besupplied to the bearings 5 and 6, the crank chamber 2a, the swash platesupport 12, etc. A second oil passage 28 is connected between the bottomof the crank chamber 2a and the suction port 28a of the pump 27. A thirdoil passage 29 is connected between the discharge port 29a of the pump27 and the first oil passage 30. As shown in FIGS. 1 and 2, a firstvalve assembly 31 is provided in the third oil passage 29. This firstvalve assembly 31 is connected via a fourth oil passage 32 to thepressure chamber 26.

As shown in FIG. 6, first and second valve chambers 34 and 35 are formedin a valve case 33. A columnar shaped first valve 36 and a sphericalshaped second valve 37 are respectively disposed in the valve chambers34 and 35. The second valve 37 is urged by a spring 38 in a direction toclose the fourth oil passage 32.

An electromagnetic solenoid 39 is secured on the top of the case 33, anda fixed core 41 and a movable core 42 are retained in the solenoid 39. Ahole 41a is formed in the fixed core 41, with a first rod 43 inserted inthe hole 41a in a lengthwise direction. The first rod 43 has a first endportion fixed to the movable core 42 and a second end portion abuttingon the second valve 37. The first valve 36 is secured to the second endportion of the first rod 43.

As shown in FIG. 6, with the solenoid 39 de-excited, the movable core 42is separated from the fixed core 41 by the urging force of the spring38. This allows the second valve 37 to be held at the position to closethe fourth oil passage 32 and for the first valve 36 to be held at theposition in order to open the third oil passage 29. The oil is suppliedto the passage 30 of the drive shaft 4 from the passage 29 to lubricatethe individual sliding portions in the compressor as shown in FIG. 1.

With the solenoid 39 excited, as shown in FIG. 7, the movable core 42 isattracted to the fixed core 41 against the urging force of the spring38. This permits the first valve 36 to be shifted to the position toclose the third oil passage 29. At the same time, the second valve 37 isshifted to the position to open the fourth oil passage 32. The oilprovided from the pump 27 is not supplied to the first oil passage 30,but is supplied into the pressure chamber 26 via the fourth oil passage32. The spool 24 therefore moves forward to shift the swash platesupport 12 in the same direction. This causes the swash plate 13 to moveto the inclined position from the upright position.

As shown in FIG. 2, a first gas passage 44 is connected between thedischarge chamber 3b and the crank chamber 2a. A second gas passage 45is connected to the suction chamber 3a and the crank chamber 2a. Asshown in FIG. 6, the first gas passage 44 and the second gas passage 45are in partial communication with each other. A second valve assembly 46is provided midway in the first gas passage 44. Both the first andsecond valve assemblies 31 and 46 utilize the electromagnetic solenoid39.

As shown in FIG. 6, a valve chamber 48 is formed in a valve case 47 ofthe second valve assembly 46. A spherical valve 49 is disposed in thevalve chamber 48. A spring 50 urges the valve 49 to close the passage44. A second rod 51 is fixed to the movable core 42 and abuts on thevalve 49.

With the solenoid 39 excited, as shown in FIG. 7, the second rod 51moves, together with the movable core 42, away from the valve 49.Concurrently, spring 50 urges the valve 49 to close the passage 44.

When the solenoid 39 is de-excited during a compression cycle with theswash plate 13 inclined, the second rod 51, as shown in FIG. 6, is movedupward by the urging force of the spring 38 via the second valve 37, thefirst rod 43 and the movable core 42. This configuration is also shownin FIG. 8. Accordingly, the valve 49 is shifted to the position to openthe passage 44. Consequently, the high-pressure gas is supplied via thepassage 44 to the crank chamber 2a from the discharge chamber 3b, thusincreasing the differential pressure Δp between the pressure in thecrank chamber 2a and the pressure in the suction chamber 3a, which actson each piston 17. The swash plate 13 is therefore forced to move to theupright position from the inclined position.

During the compressor's compression cycle, the displacement alteringcontrol is performed on the compressor in accordance with the coolingload. In accordance with the value of the suction pressure proportionalto the cooling load, the degree of the opening of the passage 45, whichis connected to the crank chamber 2a and suction chamber 3a, isadjusted. As a result, an adjustment is made to the differentialpressure Δp acting on the piston 17.

As shown in FIG. 6, a third valve assembly 52 is located between thefirst and second valve assemblies 31 and 46. A retainer chamber 47a isformed in the case 47. A valve 53 is disposed in the retainer chamber47a to open or close the passage 45. This valve 53 is urged by a spring54 in a direction to close the passage 45. A chamber 55 is defined bythe valve 53 and the case 47. The suction pressure in the suctionchamber 3a is applied inside the chamber 55 via the passage 45. Achamber 75, formed in the case 47, communicates with the crank chamber2a.

The degree of opening of the passage 45 is controlled based on thedifference between the pressure in the chamber 55 and that in thechamber 75. This chamber 55 communicates with a chamber 47b, definedbetween the inner surface of the valve 53 and a bellows 56, via apassage 53a formed in the valve 53. The second rod 51 is slidablyinserted through a hole 53b formed in the valve 53.

With a large cooling load and a high pressure in the suction chamber 3a,a large pressure is created in the chamber 55 causing the valve 53 toopen. Therefore, a large amount of gas flow into the suction chamber 3avia the passage 45 from the crank chamber 2a. As a result, thedifferential pressure p acting on the piston 17 decreases, causing theinclined angle of the swash plate 13 to increase. This in turn resultsin an increase in the stroke of the piston 17 as well as in an increasein the compressor's displacement.

When the cooling load becomes smaller and the pressure in the suctionchamber 3a falls, on the other hand, the pressure in the chamber 55 alsodrops. Accordingly, the valve 53 is shifted in a direction thatrestricts the passage 45. This increases the differential pressure pwhich in turn reduces the inclined angle of the swash plate 13 and thestroke of the piston 17. The compressor can thus operate with a smalldisplacement.

A passage provided between the crank chamber 2a and the suction chamber3a includes a restriction (not shown). Accordingly, blow-by gas enteringthe crank chamber 2a, passing between the inner surface of each cylinderbore 1a and the associated piston 17, circulates back to the suctionchamber 3a.

As shown in FIG. 6, a controller 57 as control means, electricallyconnected to the coil 40, of the electromagnetic solenoid 39, comprisesa central processing unit (CPU) 58 and a timer 59. The controller 57receives various electrical signals from an ignition switch 62 for theengine, an air conditioning switch 63, a sensor 64 for detecting thetemperature of the gas discharged from the compressor, a sensor 65 fordetecting the temperature inside the vehicle, a suction pressure sensor(not shown), a discharge pressure sensor (not shown), and the like. Thetimer 59 executes a counting operation to set the operation start timingand the operation time for the electromagnetic solenoid 39. When the airconditioning switch 63 is switched on, the electromagnetic solenoid 39is energized.

The CPU 58 has a memory 66 which stores various kinds of data.

The operation of the thus constituted variable displacement compressorwill be now described.

When the engine starts while the air conditioning switch 63 is switchedoff, the drive shaft 4 of the compressor rotates. The ON signal from theengine ignition switch 62 is transferred to the controller 57, causingthe electromagnetic solenoid 39 to be excited for a predetermined time,e.g., 10 minutes. This time is set by the timer 59, under the control ofthe CPU 58.

Consequently, as shown in FIG. 7, the movable core 42 is attracted tothe fixed core 41, so that the first valve 36 is positioned to close thethird oil passage 29, and the second valve 37 is positioned to open thefourth oil passage 32. Therefore, the pump 27 supplies the oil to thepressure chamber 26 via the fourth oil passage 32.

As a result, the spool 24 moves forward, shifting the swash plate 13forward to the inclined position indicated by the chain line in FIG. 1from the upright position indicated by the solid line in this diagram.The spool 24 moves forward until it hits against the stopper 19. At thistime, the large-diameter portion 24a comes off the center hole 1b,permitting the oil in the pressure chamber 26 to flow into the crankchamber 2a. As indicated by the chain line in FIG. 1, the inclined angleof the swash plate 13 is not large.

As the drive shaft 4 rotates, the piston 17 reciprocates in theassociated cylinder bore 1a, causing the gas to be supplied into thecylinder bore 1a from the external refrigerant circuit via the suctionchamber 3a. The supplied gas is compressed in the cylinder bore 1a andis then discharged to the external refrigerant circuit via the dischargechamber 3b. Because the inclined angle of the swash plate 13 is notlarge at this time, the compressor will run with a small displacement.

The excited electromagnetic solenoid 39 moves the second rod 51 togetherwith the movable core 42 downward in FIGS. 6 and 7. At the same time,the spring 50 urges the valve 49 of the second valve assembly 46 to aposition to close the passage 44. Consequently, the gas supply to thecrank chamber 2a from the discharge chamber 3b is stopped.

After the elapse of a predetermined time (e.g., about 10 minutes), thetimer 59 de-excites the electromagnetic solenoid 39 upon time-up.Consequently, the first valve 36 of the first valve assembly 31 is urgedin the direction that opens the third oil passage 29, while the secondvalve 37 is urged in the direction that closes the fourth oil passage 32as shown in FIG. 6. This inhibits the oil supply to the pressure chamber26, thereby freeing the spool 24.

The second rod 51 causes the valve 49 of the second valve assembly 46 tomove in the direction to open the passage 44 against the urging force ofthe spring 50. This allows high-pressure gas to be supplied into thecrank chamber 2a from the discharge chamber 3b, thus increasing thedifferential pressure Δp that acts on the piston 17. As a result, theswash plate 13 is forced to return to the upright position, causing thecompressor to be switched to the zero-displacement operation mode.

Under the zero-displacement operation, the pressure in the dischargechamber 3b drops, reducing the differential pressure Δp. Since thecenter of gravity of the swash plate 13 lies opposite the hingemechanism with respect to the drive shaft 4, the swash plate 13 is heldat the upright position due to the centrifugal force acting on thegravitational center of the swash plate 13.

As described above, when the compressor is activated, the compressortemporarily runs with a small displacement, e.g., 10%. Therefore, theoil laden gases in the condenser and evaporator are supplied to thesuction chamber 3a. The oil laden gas is also blown by to the crankchamber 2a from the compression chamber in the associated cylinder bore1a, passing through the clearance between the outer surface of theassociated piston 17 and the inner surface of the associated cylinderbore 1a.

The liquid refrigerant in the crank chamber 2a, together with that gas,flows via the passage 45 into the suction chamber 3a from which it issupplied into the cylinder bore 1a. The liquid refrigerant is thendischarged from the cylinder bore 1a. Accordingly, the lubricatingoil-containing liquid refrigerant in the crank chamber 2a is graduallygone. In the above-described manner, the gas circulates between thecompressor and the external refrigerant circuit, so that the oil and gasin the external refrigerant circuit return to the compressor.

When the air conditioning switch 63 is switched on, the controller 57keeps the electromagnetic solenoid 39 excited, permitting the continualsupply of the lubricating oil to the pressure chamber 26 from the pump27. The spool 24 is therefore held at the forward position. At thistime, the swash plate 13 turns while its inclined angle is beingadjusted in accordance with the cooling load. This reciprocates thepiston 17 to execute the gas compression stroke.

During this operation, the degree of opening of the passage 45 isadjusted by the third valve assembly 52 in accordance with a change inthe suction pressure that is proportional to the cooling load.Consequently, the differential pressure Δp acting on the piston 17 isadjusted. In accordance with the cooling load, therefore, the inclinedangle of the swash plate 13 is altered to adjust the dischargedisplacement.

When the temperature inside the vehicle is low and the cooling load issmall, the pressure in the suction chamber 3a is low so that the degreeof opening of the passage 45 is reduced by the valve 53 of the thirdvalve assembly 52. As a result, the differential pressure Δp acting onthe piston 17 is kept large so that the swash plate 13 is held at theminimum inclined angle for the 10% displacement operation.

When the cooling load is large, on the other hand, the pressure in thesuction chamber 3a is high so that the degree of opening of the passage45 is increased by the valve 53 of the third valve assembly 52, thusreducing the differential pressureΔp. Consequently, the swash plate 13is moved away from the spool 24 to the maximum inclination side. Whenthe cooling load is large, generally speaking, the air conditioningswitch 63 is switched on, so that the compressor runs with a largedisplacement upon the activation of the engine.

When the zero-displacement operation continues for a predetermined time,i.e., when the de-excitation state of the electromagnetic solenoid 39continues for a given time (e.g., 10 to 30 minutes) after the airconditioning switch 63 is switched off, the swash plate 13 istemporarily inclined by the timer 59 to accomplish the operation undercompression. In other words, the electromagnetic solenoid 39 is excitedfor a predetermined time, e.g., 10 minutes, set by the timer 59, underthe control of the CPU 58.

Consequently, as mentioned earlier, the movable core 42 is attracted tothe fixed core 41, so that the first valve 36 is positioned to close thethird oil passage 29, and the second valve 37 is positioned to open thefourth oil passage 32. Therefore, the pump 27 supplies the oil to thepressure chamber 26 via the fourth oil passage 32.

As a result, the spool 24 moves forward, shifting the swash plate 13 tothe inclined position indicated by the chain line in FIG. 1 from theupright position indicated by the solid line in this diagram. As thedrive shaft 4 rotates, therefore, the gas circulates between thecompressor and the external refrigerant circuit, ensuring richlubrication inside the compressor.

When the predetermined time elapses, the timer 59 de-excites theelectromagnetic solenoid 39 upon time-up. Consequently, the second rod51 causes the valve 49 of the second valve assembly 46 to move in thedirection to open the passage 44 against the urging force of the spring50. High-pressure gas is therefore supplied into the crank chamber 2afrom the discharge chamber 3b, thus increasing the differential pressureΔp that acts on the piston 17. As a result, the swash plate 13 is forcedto return to the upright position, causing the compressor to be switchedto the zero-displacement operation mode.

In short, when the compressor according to this embodiment is calledupon to run in the zero-displacement mode when the air conditioningswitch 63 is set off, the compressor is shifted to thesmall-displacement state every given period of time, allowing the gas tocirculate between the compressor and the external refrigerant circuit.The sliding portions inside the compressor are therefore welllubricated. Because this periodic operation every given period of timeis carried out with a small displacement, the load on the engine issmall.

This invention is not limited to the above-described embodiment, but maybe embodied in the following forms without departing from the spirit andscope of the invention.

(1) A spring 133 may be disposed in the pressure chamber 26 to urge thespool 24 forward while the compressor is not running, as shown in FIG.9.

With this structure, when the compressor is running, the inclined angleof the swash plate 13 is controlled as per the above-describedembodiment. When the compressor is not running, the swash plate 13 isheld at the minimum inclination position by the spring 133. When theengine is activated, therefore, the compressor spontaneously startsrunning with a small displacement, thus further improving thelubrication performance at the individual sliding portions in the crankchamber 2a.

(2) In the above-described embodiment, the valve 53 to open or close thesecond passage 45 is opened or closed in accordance with the suctionpressure. Instead of the use of the suction pressure, an electromagneticvalve may be used so that the valve 53 is opened or closed by anexternally supplied signal.

We claim:
 1. A compressor having a drive shaft rotatably supported in ahousing, a swash plate mounted on for rotation with said drive shaft,and a piston slidably accommodated in a cylinder bore, rotation of theswash plate with said drive shaft being converted to reciprocatingmovement of the piston in the cylinder bore to compress gas containingoil mist which, upon circulation within the compressor, lubricatescomponent parts of said compressor in moving contact with each other,said swash plate being tiltable between an upright position normal tothe drive shaft and a range of inclining positions with respect to thelongitudinal axis of the drive shaft to increase displacement of thecompressor, and wherein compressed gas is discharged from a dischargechamber, said compressor comprising:means for forcibly operating theswash plate to incline the swash plate from the upright position whensaid swash plate would otherwise be caused to assume the uprightposition to thereby compress and circulate within the compressor gascontaining oil mist, whereby the oil mist is supplied to said componentparts.
 2. The compressor as set forth in claim 1, wherein said means forforcibly operating the swash plate temporarily inclines the swash platefrom the upright position when the compressor is driven.
 3. Thecompressor as set forth in claim 2, wherein said means for forciblyoperating the swash plate temporarily inclines the swash plate from theupright position starting with the moment the compressor commences to bedriven.
 4. The compressor as set forth in claim 1, further comprising:acrank chamber defined in the housing and accommodating said swash plate;and means for inclining the swash plate throughout said range ofinclining positions, which means includes a gas passage communicatingbetween said discharge chamber and said crank chamber for supplying saiddischarged compressed gas to the crank chamber from the dischargechamber, and means for controlling the flow of compressed gas throughsaid crank chamber whereby an inner pressure of the crank chamber isvaried for changing the inclining position of the swash plate.
 5. Thecompressor as set forth in claim 4, wherein said means for forciblyoperating the swash plate includes a switchable electromagnetic valveconnected to said gas passage.
 6. The compressor as set forth in claim1, wherein said housing includes a central hole accommodating a spooldisposed for movement axially along a radially outer surface of thedrive shaft;said compressor includes a support member for supporting theswash plate, and said means for forcibly operating the swash plateincludes means for moving the spool to engage said support member todrive said support member to incline the swash plate.
 7. The compressoras set forth in claim 6, wherein said spool has a radially outercylindrical surface;said central hole has a radially inner cylindricalsurface; said compressor includes a pressure chamber defined betweensaid cylindrical surfaces; and a hydraulic pump is connected to thepressure chamber, said pump being arranged to be actuated by therotation of the drive shaft.
 8. The compressor as set forth in claim 7,further comprising:an oil passage extending in the drive shaft along thelongitudinal axis of the drive shaft, said passage having openings forcommunicating with the component parts, wherein said hydraulic pumpsupplies the oil mist to the component parts by way of the oil passage.9. The compressor as set forth in claim 8, further comprising a valveconnecting the hydraulic pump with either the pressure chamber or theoil passage.
 10. The compressor as set forth in claim 7, furthercomprising a spring accommodated in the pressure chamber to hold theswash plate at a minimum inclining position by means of the spool whenthe compressor is at a standstill.
 11. A compressor having a drive shaftrotatably supported in a housing, a swash plate mounted on for rotationwith said drive shaft, and a piston slidably accommodated in a cylinderbore, rotation of the swash plate with said drive shaft being convertedto reciprocating movement of the piston in the cylinder bore to compressgas containing oil mist which, upon circulation within the compressor,lubricates component parts of said compressor in moving contact witheach other, means for forcibly operating said swash plate to incline theswash plate between an upright position normal to the drive shaft and arange of inclining positions with respect to the longitudinal axis ofthe drive shaft to increase displacement of the compressor, and whereincompressed gas is discharged from a discharge chamber, said compressorcomprising:a crank chamber defined in the housing and accommodating saidswash plate; gas passages communicating between said discharge chamberand said crank chamber for supplying said discharged compressed gas tothe crank chamber from the discharge chamber; and means for controllingthe flow of compressed gas through said gas passages for temporarilyoperating the swash plate to an inclined position when said swash platewould otherwise be caused to assume the upright position by an innerpressure of the crank chamber, whereby the oil mist is supplied to saidcomponent parts.
 12. The compressor as set forth in claim 11, whereinsaid swash plate is temporarily forcibly inclined when the compressor isdriven.
 13. The compressor as set forth in claim 12, wherein said swashplate is temporarily forcibly inclined when the compressor commences tobe driven.
 14. The compressor as set forth in claim 11, wherein saidhousing includes a central hole; and wherein said compressor includes aspool accommodated in the central hole and moveable axially along aradially outer surface of the drive shaft, and a support member forsupporting the swash plate, wherein the movement of the spool drivessaid support member to incline the swash plate.
 15. The compressor asset forth in claim 14, wherein said spool has a radially outercylindrical surface and said central hole has a radially innercylindrical surface; andwherein said compressor includes a pressurechamber defined between said cylindrical surfaces, and a hydraulic pumpis connected to the pressure chamber, said pump being arranged to beactuated by the rotation of the drive shaft.
 16. The compressor as setforth in claim 15, further comprising: an oil passage extending in thedrive shaft along the longitudinal axis of the drive shaft, said passagehaving openings communicating with the component parts, wherein saidhydraulic pump supplies the oil mist to the component parts by way ofthe oil passage.
 17. The compressor as set forth in claim 16, furthercomprising a valve connecting the hydraulic pump with one of thepressure chamber and the oil passage.
 18. A compressor having a driveshaft rotatably supported in a housing, a swash plate mounted on saiddrive shaft for rotation therewith, and a piston slidably accommodatedin a cylinder bore, rotation of the swash plate with said drive shaftbeing converted to reciprocating movement of the piston in the cylinderbore to compress gas including oil mist for lubricating sections of thecompressor each section including a set of component parts in movingcontact with each other, said swash plate being tiltable between anupright position normal to the drive shaft and a range of incliningpositions with respect to the longitudinal axis of the drive shaft toincrease displacement of the compressor, and wherein compressed gas isdischarged from a discharge chamber, said compressor comprising:a crankchamber defined in the housing and accommodating said swash plate; gaspassages communicating between said discharge chamber and said crankchamber for supplying discharged compressed gas to the crank chamberfrom the discharge chamber; means for controlling the flow of compressedgas through said gas passages whereby an inner pressure of the crankchamber is varied for operating the swash plate to a range of inclinedpositions; said housing including a central hole with a radially innercylindrical surface; a spool accommodated in said central hole anddisposed for movement axially along a radially outer surface of thedrive shaft, said spool having a radially outer cylindrical surface; apressure chamber defined between said radially outer cylindrical surfaceand said radially inner cylindrical surface; a hydraulic pump connectedto supply gas under pressure to said pressure chamber, said pump beingactuated by rotation of the drive shaft; a support member for supportingthe swash plate, said supply of gas under pressure to said pressurechamber causing movement of the spool to engage said support member todrive said support member to operate the swash plate to an inclinedposition; and an oil passage extending in the drive shaft along thelongitudinal axis of the drive shaft, said passage having openings forcommunicating with the sets of component parts, said hydraulic pumpbeing disposed to supply the oil mist to the sets of component parts byway of the oil passage.
 19. The compressor as set forth in claim 18,wherein said swash plate is temporarily forcibly inclined when thecompressor is driven.
 20. The compressor as set forth in claim 19,wherein said swash plate is temporarily forcibly inclined when thecompressor commences to be driven.